Jerk nystagmus is what we are usually referring to when we say horizontal or vertical nystagmus and is described by the trajectory and the provoking factor (e.g., gaze-evoked positional). Examples of this are upbeat or vertical, downbeat, horizontal, or torsional.

Pendular nystagmus have a sinusoidal oscillation (think a sine wave as depicted below). The important fact here is that there is never a fast phase here or a “jerking.” It can move in a torsional, horizontal, vertical, or combination of these that results in various patterns (e.g., circular, elliptical). We discussed pendular nystagmus in the discussion of oculomasticatory myorhythmia seen in Whipple’s disease – more on this later.

Causes of Vertical Nystagmus

The primary source of data regarding causes of vertical nystagmus is from Baloh et al’s 1989 paper in ze French literature (Revue neurologique) that reviewed the clinical features of 106 patients (86 with vertical nystagmus) from UCLA’s Eye Movement Laboratories. The n is arguably small but the largest cohort of data that we have currently.

Key takeaways include:

Brainstem/cerebellar stroke + cerebellar degeneration account for almost half of the cases.

This finding on physical exam should prompt further evaluation for primary CNS etiologies and may include prompt advanced imaging.